scispace - formally typeset
Search or ask a question

Showing papers in "Materials Science and Technology in 1989"


Journal ArticleDOI
TL;DR: In this article, nineteen models and equations relating the degree of cracking to the fracture toughness are reviewed and then modified in a standard manner for both experimental convenience and direct comparison for both direct comparison.
Abstract: There is considerable interest in determining the fracture toughness of brittle materials by measuring the extent of cracking associated with a Vickers indentation because of the ease of specimen preparation and the simplicity of the test. However, confusion has been engendered by the multitude of models and equations in the literature relating the degree of cracking to the fracture toughness. In Part 1 of this work, nineteen of these equations are reviewed and then modified in a standard manner for both experimental convenience and direct comparison.MST/1050a

603 citations


Journal ArticleDOI
TL;DR: The standardised indentation fracture toughness equations formulated in Part 1 have been applied to a range of brittle materials: namely, glass ceramics, aluminas, zirconias, and WC-Co cermets.
Abstract: The standardised indentation fracture toughness equations formulated in Part 1 have been applied to a range of brittle materials: namely, glass ceramics, aluminas, zirconias, and WC–Co cermets. Ana...

281 citations


Journal ArticleDOI
TL;DR: In this paper, a review of existing experimental evidence on the role of reactive element oxide particles in enhancing oxidation resistance is presented. But, the authors do not consider the effect of the reactive element type, concentration, and initial distribution.
Abstract: Reactive element additions may promote the formation of protective oxide scales on high temperature alloys, and improve long term oxidation resistance by limiting the rate of scale growth and inhibiting scale failure processes. Various modifications to transport properties and mechanical behaviour have been proposed to explain the observed benefits. These mechanisms are reviewed with reference to available experimental evidence. Key steps in enhancing oxidation resistance are probably the provision of reactive element oxide particles for incorporation into a scale and consequent segregation of reactive element ions to high diffusivity pathways and interfaces. Such behaviour is consistent with known variations in protection resulting from changes in reactive element type, concentration, and initial distribution.MST/1055

182 citations


Journal ArticleDOI
TL;DR: In this paper, the formation of acicular ferrite is found to be dependent on the presence of a suitable distribution of oxide inclusions > 0·4 μm in size.
Abstract: Experimental steels similar in composition to structural grades were prepared from weld metal deposits to study the formation of acicular ferrite under conditions experienced in the heat affected zone for a range of welding processes. The formation of acicular ferrite under these conditions is found to be dependent on the presence of a suitable distribution of oxide inclusions > 0·4 μm in size. The characteristics and proportion of acicular ferrite in the microstructure also depend on the prior austenite grain size and cooling rate. The relationship between these factors is presented in a simplified quantitative model, which is supported by data from limited welding trials. Metallographic observations suggest that acicular ferrite forms in two stages. The first involves the formation of relatively large primary acicular ferrite plates by multiple nucleation at intragranular inclusion sites, and the second involves the formation of many smaller acicular ferrite grains that grow sympathetically from...

172 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the wear resistance of an alumina fiber-aluminum metal matrix composite system to wear by two-body abrasion and found that wear resistance ranges from almost two to six times that of the unreinforced matrix alloy.
Abstract: Investigations are reported of the response of an alumina fibre–aluminium metal matrix composite system to wear by two-body abrasion. The wear resistance of the composites was found to range from almost two to six times that of the unreinforced matrix alloy. A transition in wear behaviour was found for the various sizes of abrasive particle. With small particles, the wear resistance of the composite increased with increasing fibre volume fraction and the worn surfaces were relatively smooth. With larger particles, the wear resistance decreased with increasing fibre content above a certain level and, on the worn surfaces, fibre fracture and extensive debonding were observed at the fibre/matrix interface. The effect of abrasive particle size on this transition behaviour may be explained by a theoretical analysis of the fracture of a brittle fibre in a ductile matrix under point loading.MST/872

164 citations


Journal ArticleDOI
TL;DR: In this article, the effects of conventional rolling and cross-shear rolling (i.e. between rolls of differing peripheral speeds) on roll force and bonding strength are critically compared, and the incorporation of an optimum final heat treatment considerably decreases the requirement on rolling.
Abstract: The successful production of wide bimetallic sheets and strips by cold roll cladding depends on the technical solution of reduction of rolling load while still guaranteeing good bond quality. In the present paper, systematic experimental data on the cold roll cladding of aluminium–stainless steel, copper–stainless steel, and mild steel–stainless steel are correlated and the basic mechanism is discussed, aided by a scanning electron microscopy study of the separated interface. The effects of conventional rolling and cross-shear rolling (i.e. between rolls of differing peripheral speeds) on roll force and bonding strength are critically compared. It is found that use of the cross-shear cold rolling technique results in a significant reduction in rolling load for equal primary bonding strength and that the incorporation of an optimum final heat treatment considerably decreases the requirement on rolling.MST/971

103 citations


Journal ArticleDOI
TL;DR: In this article, the formation of the protective scales on iron and nickel base alloys is discussed, with particular reference to the population densities of the initial nuclei of the oxide and the rates of growth and coalescence of these particles to develop the healing barrier layer.
Abstract: Some of the important principles of alloy oxidation are discussed, with emphasis on the formation of protective Cr2O3, Al2O3, and SiO2 scales on iron and nickel base alloys. The competition between internal and external oxidation is considered and it is shown how establishment of the protective layer is influenced by various parameters, including alloy interdiffusion coefficient, oxygen solubility and diffusivity in the alloy, and the relative growth rates of the various oxides. The importance of the transient stage of oxidation is emphasised, with particular reference to the population densities of the initial nuclei of the protective oxide and the rates of growth and coalescence of these particles to develop the healing barrier layer. Consideration is given to the effectiveness of the protective scales in service, with respect to transport processes and mechanical integrity. The influence of the minor alloying elements, manganese, titanium, aluminium, silicon, molybdenum, and niobium, on oxidati...

96 citations


Journal ArticleDOI
TL;DR: A review of the state of the art in coating technology can be found in this paper, where various methods of forming a coating which have been developed are described and an attempt is made to indicate their relative advantages and disadvantages.
Abstract: This review considers the present state of coating technology. The various methods of forming a coating which have been developed are described and an attempt is made to indicate their relative advantages and disadvantages. Many of these methods are well established industrial practice, while others are only at the laboratory stage of development. Two basic types of system are considered. In the first system, the alloy composition is optimised to give enhanced oxidation resistance using either diffusion or overlay processes; in the second system, the component is coated directly with an inert stable diffusion barrier, usually an oxide layer.MST/1042

86 citations


Journal ArticleDOI
TL;DR: In this article, the authors combined production scale experiments with laboratory examinations to investigate the effect of various material and process parameters on microstructure, texture, and earing of the resulting products.
Abstract: Control of earing behaviour at the hot band stage is a critical requirement for successful manufacture of aluminium alloy sheet for beverage cans The present study has combined production scale experiments with laboratory examinations to investigate the effect of various material and process parameters on microstructure, texture, and earing of the resulting products It is shown that optimisation of the product is strongly dependent on (i) iron content of the alloy, (ii) ingot homogenisation temperature, (iii) finish hot rolling temperature, and (iv) heating rate during hot band annealing Earing level after annealing is shown to depend on the balance between cube (+ Goss) texture intensity and the volume of material having almost randomly spread orientations Pronounced 0/90° earing tendency is usually associated with coarse and elongated grain structures A model is shown which represents the microstructure–texture evolution as a competition between cube/Goss grains, which nucleate systematica

83 citations


Journal ArticleDOI
TL;DR: In this paper, a procedure for materials selection in mechanical design is described which allows the identification, from among the full range of materials available to the engineer, the subset most likely to perform best in a given application.
Abstract: Information on material properties is essential to engineering design. The breadth and precision of the data that the designer requires depend on the stage the design has reached: at the start (the ‘conceptual’ stage), low level data for all materials; at the finish (the ‘detailed design’ stage), data at a high level of precision for one or a few materials. In this paper, a procedure for materials selection in mechanical design is described which allows the identification, from among the full range of materials available to the engineer, the subset most likely to perform best in a given application.MST/1064

83 citations


Journal ArticleDOI
TL;DR: In this article, an evaluation is made of the effect of the characteristics of raw materials on the properties of WC-Co coatings and their abrasion wear performance, and it was found that the coating characteristics were affected by the particle size, chemistry, phase composition, and porosity of the powder, factors which are dependent on the method of manufacture of powder.
Abstract: In the present paper, an evaluation is made of the effect of the characteristics of raw materials on the characteristics of plasma sprayed WC–Co coatings and their abrasion wear performance. The raw materials and the coatings were characterised using X-ray diffraction techniques and metallography. The coatings were subjected to a standard ASTM abrasion wear test and their relative performances were explained based on their characteristics. Mainly, it was found that the coating characteristics were affected by the particle size, chemistry, phase composition, and porosity of the powder, factors which are dependent on the method of manufacture of the powder. In turn, it was found that the coating characteristics such as phase composition, porosity, and carbide size affected the abrasion wear performance. In general, it appears that better abrasion wear resistance is provided by denser coatings, which have a very fine distribution of hard phases (such as η-carbides) and an absence of softer phases.MST/790

Journal ArticleDOI
TL;DR: In this article, the uniaxial tensile and plane strain fracture toughness properties are presented and the behaviour is discussed in terms of the role of the matrix and grain boundary precipitates, associated precipitate free zones (PFZs), and the occurrence of short-transverse delamination.
Abstract: Mechanisms influencing the ambient temperature mechanical properties of commercial Al–Li alloys 2090, 8090, 8091, and 2091 are examined as a function of plate orientation, with specific emphasis on the role of microstructure. In Part 1, results on the uniaxial tensile and plane strain fracture toughness properties are presented and the behaviour is discussed in terms of the role of the matrix and grain boundary precipitates, associated precipitate free zones (PFZs), and the occurrence of short-transverse delamination. It is seen that in general peak aged microstructures show an excellent combination of strength and toughness (L–T, T–L), equal to or exceeding that shown by traditional 2000 and 7000 series high strength aluminium alloys. The superior toughness of peak aged compared with naturally aged microstructures seems to be associated with widespread matrix precipitation of platelike precipitates (T1 in Al–Li–Cu alloys and S in Al–Li–Cu–Mg alloys), β′-dispersoids and second phase particles whi...

Journal ArticleDOI
TL;DR: In this article, the sequence of precipitation and its kinetics in 17-4 PH (precipitation hardening) stainless steel were studied by observing the electrical resistivity and microstructure of the alloy during isothermal aging at various temperatures in the range 320-600°C.
Abstract: The sequence of precipitation and its kinetics in 17–4 PH (precipitation hardening) stainless steel were studied by observing the electrical resistivity and microstructure of the alloy during isothermal aging at various temperatures in the range 320–600°C. By the absence of an incubation period for the onset of precipitation it is shown that there is no free energy barrier to nucleation. The electrical resistivity of the specimen decreased on prolonged aging approaching a steady value asymptotically with time. The alloys aged above 550°C were found to have higher final resistivity values than those aged at lower temperatures. By transmission electron microscopy, local reversion of the martensite to austenite, attributed to enhanced diffusion and concentration of copper atoms at the lath boundaries, was revealed in the specimens aged at temperatures above 550°C. The kinetics of precipitation in the system obeyed the Johnson–Mehl equation. The activation energy Q of the precipitation process was est...

Journal ArticleDOI
TL;DR: In this article, a Monte Carlo computer simulation technique was used to simulate pictorially grain growth and grain interactions during solidification, and it was shown that columnar to equiaxed transition occurs when the volume fraction of equiaaxed grains ahead of the columnar interface is 0·50.
Abstract: A Monte Carlo computer simulation technique, previously applied to the simulation of a number of solid state processes involving microstructural evolution, has been employed to simulate and represent pictorially grain growth and grain interactions during solidification. By careful control of the number, location, and time of origin of grain nuclei it has been possible to simulate a wide range of features of grain structure in castings. Also, in support of an existing statistical argument, it has been demonstrated that the columnar to equiaxed transition occurs when the volume fraction of equiaxed grains ahead of the columnar interface is 0·50.MST/912

Journal ArticleDOI
TL;DR: In this paper, it was found that the strength-ductility combination (expressed numerically as tensile strength × uniform elongation) of hot rolled 0·1C-5Mn steels, with or without 2%Si, is greatly improved if an optimum reheating treatment in the range 650-675°C is applied to the steel.
Abstract: As a result of investigations into the improvement of the strength–ductility characteristics of some C–Mn steels, it has been found that the strength–ductility combination (expressed numerically as tensile strength × uniform elongation) of as hot rolled 0·1C–5Mn steels, with or without 2%Si, is greatly improved if an optimum reheating treatment in the range 650–675°C is applied to the steel. Since there is a direct connection with a large increase in the work hardening rate, it is very likely that this improvement is the result of the transformation induced plasticity of well stabilised austenite which has been formed by the reheating treatment.MST/798

Journal ArticleDOI
TL;DR: In this paper, it was shown that the addition of small amounts of Si can dramatically improve the oxidation resistance of Fe and Fe-Cr steels and also become virtually immune to breakaway oxidation in high pressure CO2, and the critical Si content for this behaviour was found to vary with the Cr content (wt-%) of the steel, from about 2·5% for mild steel to 0·7% for 9%Cr steel.
Abstract: The addition of small amounts of Si can dramatically improve the oxidation resistance of Fe and Fe–Cr steels. It is found that steels with Si contents above a certain critical value oxidise at a much slower rate and also become virtually immune to breakaway oxidation in high pressure CO2, The critical Si content for this behaviour is found to vary with the Cr content (wt-%) of the steel, from about 2·5% for mild steel to 0·7% for 9%Cr steel to 0·3% for 11%Cr steel in the temperature range 575–650°C. The lower Si content required for Cr steels than for mild steels is advantageous, because it is small enough not to degrade the other metallurgical properties such as creep strength. The beneficial effect of Si is thought to arise from the formation of a near continuous ‘healing’ layer of amorphous SiO2 at the oxide/metal interface which acts as a diffusion barrier to further transport of metal ions to the scale. The conditions required for the development of such layers are analysed using standard mo...

Journal ArticleDOI
TL;DR: A review of the toughness properties of metal matrix composites is presented in this paper, where it is shown that the toughness of MMCs is controlled by a complex interaction between the properties of the constituent phases and the processing route and no single parameter is capable of describing all the features of their toughness response.
Abstract: A review of the toughness properties of metal matrix composites (MMCs) is presented It is shown that the toughness of MMCs is controlled by a complex interaction between the properties of the constituent phases and the processing route and that no single parameter is capable of describing all the features of their toughness response It is proposed that the toughness of MMCs is best characterised by a combination of the fracture toughness and the energy values associated with the initiation and propagation of fracture This approach is used to illustrate methods of optimising toughness in MMCsMST/828

Journal ArticleDOI
TL;DR: In this article, an equation for the half width of an adiabatic shear band formed under combined stresses is derived and the importance of strain rate, stress, temperature rise, and thermal conductivity is described.
Abstract: An equation for the half width of an adiabatic shear band formed under combined stresses is derived. The importance of strain rate, stress, temperature rise, and thermal conductivity is described. Confirmation is found for the proposition that shear band width is independent of stress state and this is confirmed by comparing the theory with the experimental results of other workers.MST/933

Journal ArticleDOI
TL;DR: In this paper, the role of silicon in the oxidation of a series of 20Cr−25Ni niobium stabilised steels containing silicon in a range 0 −2·25 wt-% is explored.
Abstract: In this paper, the role of silicon in the oxidation of a series of 20Cr–25Ni niobium stabilised steels containing silicon in the range 0–2·25 wt-% is explored. Oxidation tests were carried out in thermobalances at 900°C in a CO2 based gas at 1 atm (~100 kPa) total pressure for exposure periods extending to 1·12 × 106 s (310 h). The oxidation kinetics were parabolic in all cases with a rate constant that achieved a minimum value in alloys containing ~0·6 wt-%Si. By contrast, the extent of oxide spallation on cooling was least in the silicon free and dilute alloys and increased progressively with increasing silicon level. The results are discussed in relation to the morphology of the oxide layers. Comparison is also made with a previously published complementary study on steels of similar composition, but containing a dispersion of titanium nitride particles.MST/1018

Journal ArticleDOI
TL;DR: In this paper, the phase diagram for high purity Ti-V alloys containing a stable α+β phase field with a β transus decreasing with increasing vanadium content is presented.
Abstract: Phase transformations in Ti–50V alloys containing oxygen in the range <0·095–0·36 wt-% have been studied at 750 and 400°C for times up to 1000 h. Results of electron microscopy, X-ray diffraction, and hardness testing indicate that oxygen widens the α+β phase field at 750°C and the metastable β phase miscibility gap at 400°C. The evidence is consistent with a phase diagram for high purity Ti–V alloys containing a stable α+β phase field with a β transus decreasing with increasing vanadium content. No evidence was obtained consistent with a β monotectoid form of diagram which has recently been proposed.MST/1039

Journal ArticleDOI
TL;DR: In this paper, a finite difference method is used for calculating the rate at which alloying elements redistribute between ferrite and cementite, subject to the thermodynamic constraints which determine the equilibrium compositions of these phases.
Abstract: An attempt has been made to model the kinetics of changes of composition in cementite during the aging of creep resistant low alloy steels of the type used in power plant. In the model a finite difference method is used for calculating the rate at which alloying elements redistribute between ferrite and cementite, subject to the thermodynamic constraints which determine the equilibrium compositions of these phases. It has also been possible to derive approximate analytical solutions which give good physical insight into the factors controlling the approach to equilibrium. Particle size has been found to have a strong influence on the rate at which the cementite composition is changed. A theoretical basis for the time dependence of cementite composition is also provided. The method is easily adapted to multiple or anisothermal heat treatments. Further work is suggested to account for simultaneous coarsening and changes in composition and also to allow for the formation of alloy carbides at long ag...

Journal ArticleDOI
TL;DR: In this paper, the injection of SiC particles (150 μm size) into laser surface melted commercial purity titanium, Ti-6Al-4V (wt-%) alloy, and Ti-2·5Cu (wt%) alloy has been investigated using 1·75 kW laser power, 5 mm beam diameter, 0·15 g s−l powder flowrate and traverse speeds ranging from 7 to 20 mm −l.
Abstract: The injection of SiC particles (150 μm size) into laser surface melted commercial purity titanium, Ti–6Al–4V (wt-%) alloy, and Ti–2·5Cu (wt-%) alloy has been investigated using 1·75 kW laser power, 5 mm beam diameter, 0·15 g s−l powder flowrate and traverse speeds ranging from 7 to 20 mm −l. Partial dissolution of SiC occurred and fine dendrites of TiC nucleated at the particle/matrix interfaces and also within the matrix. Silicon enrichment of the matrix and a eutectic constituent were observed. The microhardness of the melted zone was increased to 600–650 HV (500 g).MST/964

Journal ArticleDOI
TL;DR: In this article, an introduction to the aspects of composites and adhesive joints relevant to non-destructive testing is provided, together with a description of the types of defects that may occur.
Abstract: In this paper, an introduction to the aspects of composites and adhesive joints relevant to non-destructive testing is provided. The first part consists of a brief introduction to composites and adhesive joints, together with a description of the types of defects that may occur. In the second part, the main relevant nondestructive techniques used to identify these defects are described and the sensitivity of each method to the different types of defect is indicated.MST/941

Journal ArticleDOI
TL;DR: In this article, the basic process and mechanisms of sulphidation are reviewed and contrasted with oxidation, leading to an enunciation of the principles underlying the development of sulfidation resistance in model alloys involving "barrier layer" formation of protective sulphide(s) to inhibit the usually extraordinarily fast diffusion processes responsible for rapid wastage.
Abstract: The interaction of metallic materials with sulphur and sulphur bearing gases at elevated temperatures leading to the formation of sulphide corrosion products – sulphidation – is generally an extremely rapid process, much more so than oxidation. Conventionally developed high temperature alloys with adequate oxidation performance generally have poor resistance to sulphidation and the design of alloys or coatings to withstand such aggressive environments represents a major technological challenge. The basic process and mechanisms of sulphidation are reviewed and contrasted with oxidation, leading to an enunciation of the principles underlying the development of sulphidation resistance in model alloys involving ‘barrier layer’ formation of protective sulphide(s) to inhibit the usually extraordinarily fast diffusion processes responsible for rapid wastage. Underlying principles for the development of sulphidation resistant alloys are shown with reference to the behaviour of various experimental model M...

Journal ArticleDOI
TL;DR: The results of an investigation of the orientation relationships between adjacent plates of acicular ferrite are reported in this article in an attempt to elucidate further the mechanism of ferrite formation.
Abstract: The results of an investigation of the orientation relationships between adjacent plates of acicular ferrite are reported in an attempt to elucidate further the mechanism of acicular ferrite formation. Welds were made using the manual metal arc technique and the as deposited microstructure of the high strength steel weld deposits was examined using crystallography and transmission electron microscopy. It was found that clusters of acicular ferrite form in such a way that adjacent plates tend to have a similar orientation in space; the reasons for this are discussed.MST/903

Journal ArticleDOI
TL;DR: In this paper, an investigation has been carried out into the oxidation behavior of 310 stainless steel and 321 stainless steel in oxygen at 800 and 1000°C, respectively, and the results show that the more slowly growing nodules are healed by an Fe-Cr spinel oxide, although this is less effective than a Cr2O3 layer.
Abstract: An investigation has been carried out into the oxidation behaviour of 310 stainless steel and 321 stainless steel in oxygen at 800 and 1000°C. Both steels contain sufficient chromium to ensure development of a protective Cr2O3 rich scale in the early stages. However, the oxide growth process results in development of blisters in the scale, as parts of it develop out of contact with the steel surface. Mechanical failure of these features allows access of oxygen to a chromium depleted steel surface. In 310 stainless steel, there is sufficient chromium to ensure re-establishment of a Cr2O3 rich scale at 1000°C but, in 321 stainless steel, this is not always the case and rapid growth of iron rich oxide nodules dominates the oxidation process after periods of up to 1000 h. At 800°C, there are fewer differences in the performances of the two steels. In both cases, the more slowly growing nodules are healed by an Fe–Cr spinel oxide, although this is less effective than a Cr2O3 layer. Consideration is als...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the superplastic deformation and cavitation behavior of a 7475 high strength aluminium alloy in uniaxial tension and concluded that cavitation can be significantly reduced and even eliminated.
Abstract: This investigation deals with superplastic deformation and cavitation behaviour of a 7475 high strength aluminium alloy in uniaxial tension. Intergranular cavitation increases sharply with strain as a result of continuous nucleation, thus limiting the ductility to relatively small strains in the superplastic range and affecting the room temperature service properties. To reduce the overall cavitation, several processes have been carried out. They involve treatments of the material with or without superimposed hydrostatic pressure and they can be applied before, during, or after deformation. The results of these processes are presented and compared. It is concluded that cavitation can be significantly reduced and even eliminated. Such a result can increase the use of superplastic forming for industrial applications in aeronautics and aerospace technology.MST/985

Journal ArticleDOI
TL;DR: In this paper, an experimental apparatus to examine a bond criterion is developed, and it is possible to carry out lap welding using punches that penetrate into strips of the experimental metal; these strips are simultaneously extended in the direction parallel to the bonding surface by bulging.
Abstract: An experimental apparatus to examine a bond criterion is developed. Using this apparatus, it is possible to carry out lap welding using punches that penetrate into strips of the experimental metal; these strips are simultaneously extended in the direction parallel to the bonding surface by bulging. The bond strength is investigated by varying independently the virgin surface ratio α and the normal bonding pressure p. The bond efficiency η, i.e. the ratio of the bond strength to the strength of the base metal, increases with values of α and p. However, when p has a value of 75 MN m−2 the value of η is always 0% at any value of α. It is possible to commence bonding when p=112 MN m−2, a value that is nearly equal to the flow stress of the base metal Y, i.e. p/Y ≍ 1. When p > 225 MN m−2, i.e. p/Y ≥ 2, the value of η does not depend on p, but on α, i.e. bonding commences when α =20% and the value of η reaches 100% when α=55–60%. This means that it is possible to achieve efficient bonding when the value...

Journal ArticleDOI
TL;DR: In this article, the fatigue properties, deformation characteristics, and cyclic stress response of the commercial Al-Li-Cu-Mn and the experimental Al-Lithium-Aluminum-Zr alloys cycled to failure are compared over a range of plastic strain amplitudes in various environments, spanning the inert to the very aggressive.
Abstract: The emergence of lithium containing aluminium alloys as potential light metals for aircraft structures has engendered an unprecedented widespread interest aimed at improving their mechanical properties and studying their cyclic fatigue characteristics. The phenomenon of fatigue is environment sensitive and the alternating moisture conditions experienced by this candidate airframe material can be a handicap when designing for enhanced fatigue resistance. In this paper, the fatigue properties, deformation characteristics, and cyclic stress response of the commercial Al–Li–Cu–Mn and the experimental Al–Li–Mn and Al–Li–Cu–Mg–Zr alloys cycled to failure are compared over a range of plastic strain amplitudes in various environments, spanning the inert to the very aggressive. Abnormal plastic strain–fatigue life behaviour was observed for all the alloy systems and is attributed to differences in the distribution of deformation as a function of plastic strain amplitude and to change in the relative amount...

Journal ArticleDOI
TL;DR: In this article, the phenomenon of liquid crystallinity is described and the way in which it improves the mechanical properties and processability of polymers is explained, particularly those involved in the synthesis of commercially available materials.
Abstract: It is relatively recently that thermotropic liquid crystal polymers for load bearing applications have become commercially available. These materials possess good mechanical properties and excellent processability and are intended for use at elevated temperatures in harsh chemical environments. In this paper, the phenomenon of liquid crystallinity is described and the way in which it improves the mechanical properties and processability of polymers is explained. The synthetic strategies involved in obtaining nematic mesophases in polyesters are discussed fully, particularly those involved in the synthesis of commercially available materials. The future of these new types of engineering thermoplastic will depend on cost and on the appropriate application of the unique properties they offer.MST/875